In general, aircrafts are not provided with a lavatory window. For example, large size aircrafts do not have a window located in the lavatory because the lavatory is typically a closed small chamber in its cabin area to preserve a passenger's privacy. Various kinds of lights are used in an airplane lavatory; however, the lavatory is oftentimes underlit and such a small enclosed space with artificial lighting can make a passenger feel very cramped. On the other hand, providing a large sized window in an airplane lavatory can make it difficult to maintain the strength of the aircraft's fuselage structure and to preserve passenger's privacy. In addition, a lavatory having a large sized window has a disadvantage in terms of weight of aircraft, because the window pane is heavier than material of the aircraft fuselage. For that reason, an aircraft does not have a window in a lavatory in general. Further, direct daylight and deep shadows created by the direct daylight though a large size window can also provide an uncomfortable feeling to the passenger.